1. Field of the Invention
The present invention relates to an optical recording device and method for recording information on an optical disc having a plurality of recording layers, and more particularly to optimum power control (OPC).
2. Description of the Related Art
OPC is carried out by performing a test write on an optical disc to make an optimal calibration of the recording power before recording the intended information on the disc. In a multilayer optical disc with a plurality of recording layers, when the recording is carried out on a layer in a deep position as seen from the side of incidence of the recording light, the optimal recording power differs depending on whether or not information has already been recorded on the shallower intervening recording layers. It is therefore desirable to provide recording power settings that produce stable recording performance in the information recording area, without performance variations even when the layer or layers shallower than the recording target layer present a mixture of recorded and unrecorded states.
Japanese Patent Application Publication (JP) No. 2008-192258 (pp. 1-12, FIGS. 1-6) discloses one method of finding such settings. The test write area is divided into a plurality of subareas, information is recorded on the shallower layers so as to create a different combination of recorded and unrecorded shallower layers in each subarea, OPC is performed in each subarea, and in recording on the target layer in the information recording area, the optimum recording power found for the relevant combination is used.
JP 2008-108388 (pp. 1-12, FIGS. 1-5) discloses a method that forms a similar plurality of subareas with differing combinations of recorded and unrecorded states in the shallower layers in the test write area, performs OPC in each of the subareas, and then uses the average of the OPC results as the optimal recording power.
JP 2006-179153 (pp. 1-10, FIGS. 1-4) discloses a method that decides from the amount of light reflected from spaces whether the shallower layers are in the recorded or unrecorded state, and switches the recording power accordingly.
The methods employed in JP 2008-192258 and JP 2008-108388 are excessively time-consuming because of the time required to record information so as to form a plurality of subareas with differing combinations of recorded and unrecorded states in the shallower layers in the test write area, and then perform OPC in each subarea. With these methods too much time elapses before actual recording starts. The number of times the recording power can be optimally calibrated is also limited, because each OPC operation uses up considerable amount of disc area; consequently, the number of times additional information can be recorded on a disc is limited.
The method of JP 2006-179153, which discriminates between the recorded and unrecorded states by the amount of light reflected from spaces, is apt to discriminate incorrectly because of reflectance variations due to irregularities in the formation of the recording layers and other layers in the optical disc, in which case information cannot be recorded with the optimal recording power.